Rob A. Binkhorst

Measurement of Forces Exerted on Pedal and Crank During Work on a Bicycle Ergometer at Different Loads

SummaryForce measurements on the pedal and crank during work on a bicycle ergometer revealed that:1.Force exertion is maximal when the position of the pedal is in the front at about 90 ° to the vertical line.2.The passive (hind) leg is lifted partly by the active (force exerting) leg. This effect diminishes at higher loads.3.Peak loads in one cycle are about twice the load-setting on the specific ergometer.4.Toe-elips on the pedals are probably not always used to pull at the pedals.5.The application of force measurements in several experiments concerned with ergometry and cycling is discussed.

Cardiovascular responses in paraplegic subjects during arm exercise

SummaryThe purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20%, 40% and 6070 of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (fc) was sigificantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed inQc between P and C; however, stroke volume (SV) was significantly lower andfc significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher ϕc,max. During submaximal exercise, however, this lower SV was compensated for by a higherfc and, thus at the same submaximal oxygen uptake,Qc was similar to that in the control group.

The use of pedometer and actometer in studying daily physical activity in man. Part I: Reliability of pedometer and actometer

SummaryThe purpose of this study was a critical evaluation of pedometer and actometer for estimating daily physical activity.Both instruments were tested for reliability on a carriage with movements in different directions. To obtain comparable data of different pedometers it was necessary to adjust the spring tension very carefully. The reliability of the individual actometer was satisfactory, but there are large differences between the watches. Therefore, a correction factor (C.F.) was introduced.Some experiments were carried out on a treadmill. 9 Children (aged 5–6 years) and 6 young adult males (aged 21–31 years) walked and ran at different speeds. The energy expenditure was calculated from formulas. The pedometer overestimates the actual step rate with 0.1–0.3 counts per step during fast walking (6–9 km·h−1) and fast running (15 km·h−1). It underestimates the actual step rate with 0.2–0.7 counts per step, while walking slowly. It was shown that the pedometer does not reflect the differences in energy expenditure levels at different speed very well. The actometer units per step increases more or less proportional to the speed of walking and running. In contrast to the pedometer results the actometer results are more related to the energy expediture levels at different speed.The results of this study suggest that the actometer might be a valid indicator of the daily physical activity in terms of energy expenditure.

The use of pedometer and actometer in studying daily physical activity in man. Part II: validity of pedometer and actometer measuring the daily physical activity.

SummaryThe validity of the pedometer and actometer for estimating the daily physical activity was evaluated by means of an observation study. The physical activity in a classroom of 11 pupils of a kindergarten was assessed by means of a pedometer, actometer and by observation. Besides this an activity questionnaire was completed by the infant-quide. On basis of the individual observation it is clear that the infant-guide can give valuable information about the activity of the children at school.The results of the pedometer attached to the waist and the actometers attached to the ankle were significantly correlated with the results of the observation method. The wrist actometer showed a smaller but still significant correlation with the other variables. Implications of this findings are discussed in regard toward the physical activity. The pedometer results point out that when the percentage of intense activity is high the pedometer tends to underestimate the level of activity.The actometer results indicate that such a motion recorder gives a reliable estimation of activity in children. The findings are discussed in terms of the practical applications of the actometer in the research of daily physical activity and the physical rehabilitation treatment of certain diseases.

Cardiovascular responses in persons with paraplegia to prolonged arm exercise and thermal stress

The purpose of this study was to investigate cardiovascular responses in subjects with paraplegia (P) during prolonged upper body exercise in a hot environment. In addition, the effect of the level of the lesion on cardiovascular regulation of persons with paraplegia was studied. Four P with lesions between T2-T6 (P1), five P with T7-T8 lesions (P2), four P with lesions between T9-T12 (P3), and 10 control subjects (C) performed 45-min arm-cranking exercise at 40% of the individual peak power output, in a climatic room at 35 degrees C with a 70% relative humidity. From the 15th to the 45th min, cardiac output (Q) and oxygen uptake (VO2) remained unaltered in all subjects, except a significant decrease of Q in P1. Stroke volume (SV) decreased significantly in both P (-20%) and C (-18%) during the test. Heart rate (HR) increased in compensation for P2 (56%), P3 (65%), and C (55%), whereas HR in P1 did not increase significantly. Hemoglobin concentration changes, representing total plasma volume changes, increased significantly in P2, P3, and C but not in P1. Weight loss and sweat rate increased relative to the sensate skin area and, thus, to the level of the spinal cord lesion (P < 0.01). In conclusion, P with lesions below T6 are able to maintain a stable Q by increasing HR to compensate for the declining SV during exercise in a hot environment. P with lesions above T6 cannot fully compensate for the reduction in SV by an increase in HR, therefore, Q declines.

Haemodynamic effects of adrenaline during treatment of hypertensive patients with propranolol and metoprolol.

SummaryA double blind cross-over trial of propranolol and metoprolol was carried out in eight hypertensive patients. At the end of each four-week period of medication, blood pressure and heart rate at rest were measured, and the haemodynamic effects of adrenaline infusion were studied. At rest, propranolol and metroprolol reduced the blood pressure and pulse rate to the same degree. Adrenaline infusion during propranolol medication caused a marked increase both in systolic and diastolic blood pressure, the blood flow in the forearm was unchanged, and the calculated vascular resistance showed a marked increase. Adrenaline infusion during metoprolol medication caused a less marked increase in systolic blood pressure and the diastolic pressure remained unchanged. Blood flow in the forearm increased and the vascular resistance in the forearm tended to decrease. Adrenaline infusion, therefore, caused different haemodynamic effects during non-selective β-blockade with propranolol and during β1-selective blockade with metoprolol. It seems probable that the adrenaline infusion test is comparable with adrenaline release during stress situations and the results may indicate that a β1-selective blocker is to be preferred to a non-selective one as a therapeutic agent in the treatment of hypertension.

The effect of an anti-G suit on cardiovascular responses to exercise in persons with paraplegia.

The purpose of this study was to determine whether external pressure on legs and abdomen could prevent venous blood pooling in persons with paraplegia and thus positively affect their cardiovascular responses to arm exercise. To investigate this, five male subjects with paraplegia (P), with complete lesions between T6 and T12, and five male control subjects who were wheelchair bound (C) (due to a chronic lower extremity disability), performed submaximal arm-cranking exercise at 20%, 40%, and 60% of their maximal power output (Wmax), with and without an antigravity (anti-G) suit inflated to 52 mm Hg (1 psi). For P, higher preexercise systolic pressure (127 vs 117 mm Hg) was seen with the anti-G suit. At 40 and 60% Wmax, significantly lower heart rates (at 40% = 5.7%; at 60% = 10.6%) at similar cardiac outputs were seen for P with an anti-G suit. Although not significant, P also demonstrated higher stroke volumes at 40% (4.8%) and 60% (5.0%) Wmax with external pressure. For C, no differences in preexercise blood pressure or cardiovascular responses at all three exercise levels were seen with or without the anti-G suit. These data suggest that an inflated anti-G suit is able to prevent venous blood pooling and offers hemodynamic benefits in persons with paraplegia during submaximal arm-cranking exercise. In addition, this study reports a possible alternative to hosiery or functional neuromuscular stimulation that could be applied to all subjects with spinal cord injuries regardless of type or duration of the lesion or of muscle-atrophy.

Cardiac output in paraplegic subjects at high exercise intensities

SummaryThe purpose of this investigation was to compare cardiac output (

Hemodynamic effects of isometric exercise and mental arithmetic in hypertension treated with selective and nonselective β‐blockade

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